Bonded nonwoven sheets with a defined distribution of bond strengths



J. C. PETERSEN BONDED NONWOVEN SHEETS WITH A DEFINED March 24, 1970 DISTRIBUTION OF BOND STRENGTHS 2 Sheets-Sheet 1 Filed June 14, 1968 FIG.

0.5 AVERAGE BOND STRENGTH (),GRANS w m m g 33 52:53;

INVENTOR JOSEPH CLAlNE PETERSEN 5 AVERAGE BOND STRENGTH VARIANCE (0' a m m w 33 :Ei xofiTwE ATTORNEY J- C. PETERSEN BONDED NONWOVEN SHEETS WITH A DEFINED March 24, 1970 DISTRIBUTION OF BOND STRENGTHS 2 Sheets-Sneet 2 Filed June 14, 1968 FIG.3

20 x lo mxlo uaaouos/cnhmsnacs BOND smsnem FIBER-BREAKING smncru 60 x lo w m wwi IEE VSQm wE 20 x If) 40 x lo no. Bonus/cu? AVERAGE BOND STRENGTH (ubs), ems/cm.

INVENTOR END T'F'" FIG. 5

STRAIN JOSEPH CLAINE PETERSEN United States Patent 3,502,538 BONDED NONWOVENSHEETS WITH A DEFINED DISTRIBUTION OF BOND STRENGTHS Joseph Claine Petersen, Laramie, Wyo., assignor to E. I. du Pont de Nemours and Company, Wilmington, De]., a corporation of Delaware Continuation-impart of abandoned application Ser. No. 390,020, Aug. 17, 1964. This application June 14, 1968, Ser. No. 747,405

Int. Cl. B32b 5/16 US. Cl. 161-150 8 Claims ABSTRACT OF THE DISCLOSURE Bonded nonwoven sheets of defined bond parameters exhibit high tufted-grab-tensile strength and dye-beckwidth stability. Such sheets contain matrix fibers having an average breaking strength of at least 7 grams and a multiplicity of bonds having a strength greater than 0.1 gram, the average strength of these bonds being at least 0.9 gram and less than the matrix fiber breaking strength, the bond strength distribution being characterized by a variance of at least 4, the number of bonds being such that the product of the number of bonds per cubic centimeter and the average bond strength is greater than 5x10 g./cm. and this product divided by the fiber breaking strength is less than 9 l0 /cm.

DETAILED DESCRIPTION OF THE INVENTION This application is a continuation-in-part of my application Ser. No. 390,020, filed Aug. 17, 1964, now abandoned.

This invention relates to nonwoven sheet structures, in particular to bonded nonwoven sheets which have a combination of structural features that render such sheets particularly suitable as backings for tufted carpets.

Nonwoven sheet materials which are useful as primary backings for tufted carpets offer advantages over the known woven jute backings in such properties as dimensional stability, uniformity, supply stability, and hydrophobicity.

It has now been found that the number of bonds present in the nonwoven sheet materials and the bond strengths have a material effect on the characteristics necessary for primary backings. As the tufting needles penetrate the sheet, the fibers are displaced and they become aligned around the tufting yarns. Excessive fiber breakage occurs during this operation resulting in tufted carpets which are deficient in grab-tensile strength unless the bonds are weaker than the fibers. A very lightly bonded sheet, although permitting the fibers to move freely with a minimum of fiber breakage during the tufting operation lacks adequate sheet dimensional stability during subsequent processing. When tufted, the nonwoven sheet with too few self-bonds, undergoes shrinkage in the cross-machine direction during passage through the dye-beck.

It is a purpose of this invention to provide a nonwoven sheet material that is useful as a primary carpet backing.

It is another purpose of this invention to provide a carpet backing that can be made with comparative ease and which exhibits good tufted-grab-tensile strength and good dye-beck-width stability.

An additional purpose is to provide a nonwoven sheet which is less sensitive to damage by variations in the tufting needles such as burred, barbed, blunt, off-size, etc. needles.

Another purpose is to provide a nonwoven sheet having a combination of high tensile and tear strength.

Patented Mar. 24, 1970 "ice These and other purposes of the invention are attained by providing a nonwoven sheet comprising synthetic organic fibers having an average breaking strength of at least 7 grams, bonded by a multiplicity of bonds with a bond strength greater than 0.1 gram. In the sheets, the average bond strength of these bonds is at least 0.9 gram and less than the fiber-breaking strength, the distribution of the strength of the bonds is characterized by a variance of at least 4, the number of bonds is such that the product of the number of bonds per cubic centimeter and the average bond strength is greater than 5x10 g./cm. and this product divided by the fiberbreaking strength is less than 9x10 /cm.

The invention will be further understood by reference to the drawings in which:

FIGURE 1 is a graph showing the relationship between dye-beck-width loss of tufted nonwoven sheets and the average bond strength (S) of the bonds in the untufted sheets;

FIGURE 2 is a graph showing the relationship between the dye-beck-width loss of tufted nonwoven sheets and the variance (a in bond strength (as determined herein) in the untufted sheets;

FIGURE 3 is a graph showing the relationship between the dye-beck-width loss of tufted nonwoven sheets and the product (MS) of the number of bonds per cubic centimeter (N and the average bond strength in the untufted sheet;

FIGURE 4 is a graph showing the relationship between grab-tensile strength of the tufted nonwoven sheets and the product (NQS) divided by the fiber-breaking strength (f) in the untufted sheet;

FIGURE 5 is a typical stress-strain curve obtained in the determination of the individual bond strengths; and

FIGURE 6 is a schematic representation of a bonded sheet of the invention showing matrix fibers 1 and bonds 2.

The nonwoven sheets of this invention are composed of synthetic organic fibers which are bonded into a coherent structure. The bonds may comprise self-bonds and adhesive bonds, the latter being bonds between dissimilar materials. Considering only the bonds which have a bond strength of at least 0.1 gram, the average bond strength (S) must be at least 0.9 gram. This is the first criterion for acceptable performance of the nonwoven sheets of this invention as primary carpet backings. As indicated in FIGURE 1, an average bond strength below 0.9 gram leads to nonwoven sheets which, when tufted, exhibit excessive dye-beck-width losses. The upper limit on the average bond strength is the average fiber-breaking strength. Above this level the fibers rather than the bonds will break during tufting and this leads to a poor tufted-grab-tensile strength. The average bond strengths of preferred sheets of this invention will often be no more than about 40% of the minimum fiber breaking strength of 7 grams. Referring to FIGURE 1, it will be seen that Sample A has an average bond strength of 0.55 gram and gives a dye-beck-width loss of 26%, while Sample B, with an average bond strength of 1.2 grams, gives a low-dye-beck-width loss of 2.3%. The two samples have approximately the same number of bonds: 695x10 bonds/cm? for Sample A and 5.85x10 /cm. for Sample B. I

A second criterion for acceptable performance of the nonwoven sheets of this invention as a primary carpet backing is that the distribution of strengths of the bonds must be such that the variance is greater than 4. As indicated in FIGURE 2, dye-beck-width losses increase rapidly below this level of variance. This is the type of behavior observed with an under-bonded sheet having a variance below 4, that is, a narrow distribution of weak bonds. With overbonded sheets having a narrow distribution of very strong bonds and therefore a variance of less than 4, the tufted-grab-tensile is low. A broader distribution of bond strengths in the nonwoven sheets of this invention permits wide limits on average bond strengths and bond concentration to give good products. A narrow bondstrength-distribution product necessitates very narrow limits on the number of bonds thus requiring precise control of the bonding conditions. Certain products with a variance of bond-strength-distribution below 4 may, on occasion, give acceptatble performance as primary carpet backings. Such products are sensitive to tufting needle condition and require precise control of finishing and tufting processes.

Variance, as used herein, has its accepted meaning in statistical analysis and is defined as follows:

where is the variance,

is the arithmetic mean of the bond strengths,

s is the measured value of the individual bond strengths,

and

m is the number of measurements.

A third criterion for acceptable performance is a minimum value of the product of the number of bonds per cubic centimeter (N and the average bond strength. This product, which represents the total strength of the bonds in a cubic centimeter of the nonwoven sheet, must be at least x10 g./cm. FIGURE 3 illustrates the sharp increase in dye-beck-width loss when the value of the product (N g) is less than 5x10 g./cm. Thus, not only must average bond strength be above the minimum value of 0.9 gram, but also the bond concentration must be sufficient for the product N to satisfy the third criterion. The product is used rather than the bond concentration alone since the higher the average bond strength, the fewer bonds that are required.

A fourth criterion for acceptatble performance of the nonwoven sheets of this invention involves the upper limit on the bond concentration, the lower limit having been defined by the third criterion. In setting this upper limit, it is necessary to consider the fiber-break strength (f) in addition to the average bond strength, since a greater number of strong bonds can be tolerated with stronger fibers. It has been found that the product of the average bond strength and the bond concentration divided by the fiberbreak strength, that is N E/f, should not be greater than 9X10 /cm. This is illustrated in FIGURE 4 where it is shown that tufted-grab-tensile strength rises markedly when the value of N E/f is below 9 10 /cm. Above this level, the tufted strength of non-woven sheets is markedly lower.

As indicated above, it is necessary in order consistently to obtain overall satisfactory performance of nonwoven sheets as primary carpet backings, that all four of the structural criteria defined above be met. With this structural definition of the requirements of satisfactory nonwoven sheet materials, those skilled in the art of production of non-woven sheets will recognize several methods which can be used for the manufacture of these products. For example, nonwoven webs of fibers which will have the desired fiber-breaking strength after bonding may be bonded by a combination of resinous binders, which combination, by virtue of differences in adhesive properties among the two or more bonders being used, will lead to bonds with the required distribution of bond strengths While maintaining the required level of average bond strength. Alternately the required distribution in bond strengths may be obtained by varying the size of the bond sites over a sufficiently wide range with a single resinous binder giving the specified average bond strength level (greater than 0.9 gram but less than the fiber break strength). The bond concentration may be controlled by the quantities of binder material being used. The binder may be applied in any of the methods known in the art. This includes application from dispersion or solution, as a granular or powdery material, or as binder fibers. If required these binders can be activated by application of heat in the known manner. These bonding methods and also the known solvent-bonding and self-bonding techniques have not been used before to make products meeting the structural criteria of the products of this invention.

The nonwoven webs which are used to prepare the products of this invention can be produced by the standard techniques of the nonwoven art and can be composed of staple fibers, continuous filaments or combinations of the two. Preferred products are composed of continuous filaments having a random distribution throughout the sheet. Such materials having especially high tear and tensile strength and exhibiting isotropic properties can be made by the general procedure of British Patent 932,482 and are especially preferred for use in the nonwoven sheets of this invention. The process described in this British patent involves an integrated spinning, orientation and laydown of the filaments to give a random nonwoven web which is essentially free from filament aggregates. In this process, the freshly spun filaments are electrostatically charged and are then permitted to separate due to the applied electrostatic charge before web laydown. The type of filaments used in this invention are not critical and such synthetic organic fibers as the polyamides, such as poly(hexamethylene adipamide) and polycaproamide, polyesters such as poly(ethylene terephthalate), polyhydrocarbons, such as linear polyethylene, and isotactic polypropylene, etc., are suitable.

A particularly preferred sheet material of this invention is produced from nonwoven webs of fibers of oriented isotactic polypropylene as the matrix fibers and unoriented or low-oriented isotactic polypropylene fibers as the binder material. By virtue of the lower degree of orientation in the binder fibers, they have a lower softening point than the matrix fibers. By choosing the proper bonding temperature, bonds comprising self-bonds between the matrix fibers, self-bonds between the binder fibers, and interbonds between the matrix and binder fibers can be produced. Since these can have different bond strengths, the required variance in bond-strength distribution can be readily obtained. However, because self-bonds between the matrix fibers are involved, it is necessary when practicing this method to operate the bonding step at a Sufiiciently high temperature to obtain some degree of selfbonding between the matrix fibers. This can be readily obtained since the softening point of the low-oriented binder fibers is usually only about 5l0 C. below that of the more highly oriented fibers.

The binder fibers can be incorporated into the web as separate low-oriented fibers or as low-oriented segments of mixed-orientation fibers containing higher oriented segments as well. Either of these methods can readily be adapted for use in the aforementioned process of British Patent 932,482 for the production of continuous-filament nonwoven sheets. Separate binder and matrix filaments can be produced by using two separate spinning and drawing machines and combining the filaments prior to or during web laydown. They can also be produced by splitting the thread line from the spinneret so that a part by-passes the drawing operation. Another method involves the use of a spinneret with varying capillary geometry which produces filaments with varying responses to the drawing operation. Nonwoven webs of filaments with segments having different levels of orientation can be produced by pulsing the throughput of polymer going to the drawing operation, by pulsing the draw ratio in the drawing operation, or by variation of the drawing temperature. This latter method can be carried out by passing the filaments over a fluted feed roll in the drawing step. It has been found that these various techniques produce satisfactory mixed-orientation webs for use in producing the nonwoven sheets of this invention.

The use of fibers of mixed orientation in the webs does not necessarily result in a bonded nonwoven sheet which meets all four of the above-described structural criteria. To meet these criteria, it is necessary to carry out the bonding operation under controlled conditions. Bonding of mixed-orientation webs can be carried out with less critical temperature control than necessary with sheets prepared by self-bonding of like thermoplastic fibers. Thus a range of about 3 and preferably bonding within a range of 1 C. produces acceptable product. This wider latitude of operable bonding conditions is of great significance to the commercial manufacture of bonded nonwoven sheets, particularly for the wide widths required in primary carpet backing.

The nonwoven sheets of this invention which are designed for use as primary carpet backings will usually have a unit weight of 2 to 5 oz./yd. (68 to 170 g./m. with a preferred weight of about 3 to 4 oz./yd. (102 to 136 g./m. The denier of the matrix or high-orientation filaments in the nonwoven sheets will range from about 3 to (0.3 to 1.7 tex) with the proviso that the denier must be adequate to give a fiber-break strength of at least 7 grams. Thus, filaments of isotactic polypropylene with a tenacity of 3 grams per denier would obviously have to be at least about 3 denier (0.22 tex). A preferred range for polypropylene filaments is 6 to 9 denier (0.6-7 to 1 tex) per filament. In selecting the denier of the matrix filaments, consideration must also be given to the possible loss in tenacity during the bonding operation. The fiber-breaking strength which is significant in the characterization of the nonwoven sheets of this invention is the strength of the matrix filaments in the bonded sheet.

A method which can be used to measure the average bond strength of the bonded nonwoven sheets of this invention is described below. A sample of the bonded nonwoven sheet (2 in. X 0.125 in.) (5 cm. x 0.32 cm.) is delaminated in its thickness dimension into as many layers as can be obtained without distortion or tearing of the individual strips. The number of layers obtained will vary with the thickness of the product being tested but will usually be between 3 and 10. The purpose of delaminating and using narow samples is to obtain layers having a limited but representative number of bonds so that in the subsequent tensile test, individual bond breakage can be followed and the likelihood of multiple bonds breaking simultaneously is minimized. Each of the delaminated layers is pulled apart in an Instron Tensile Tester using a l-in. (2.5 cm.) jaw separation and a strain rate of 0.02 in. (0.05 cm.) per minute. The instrument is calibrated to 40 grams full scale, thus permitting readings down to 0.1 gram. Bonds having strengths less than 0.1 gram are not measured. A typical curve is shown in FIGURE 5. The drops in load, labeled 8,, S etc., in the figure, after the maximum stress (Fm) is reached are attributed to breakage of individual bonds.

As a delaminated layer is elongated, the resultant stress (F) is distributed over the bonds supporting the stress in the strip. At any section along the layer, the stress (P) will be distributed among the bonds supporting stress within that section. The stress potential of such section will be determined by the product of the number of bonds (N supporting the stress and their average strength When the force on the layer exceeds the value of NS for the weakest section of the layer, it will begin to fail at that point, and bonds in that section will begin to break. At higher elongations, the layer is held together by a few fibers and on continued elongation,

bonds are broken in sections further back and outside the original section of the bond breakage. This expanding area of bond breakage is not definable and some basis is needed to limit the bond-strength measurement to some small finite section which can be measured. The proper amount of elongation is determined from the maximum stress recorded (Fm) which is equal to NS for the section of the layer which breaks. Accordingly, the layer is elongated until the value of N 5 and Fm give the required agreement.

The section bond breakage is determined by taking photomicrographs of the delaminated layers before and after the bond-breaking test, comparing the same and measuring the area of disruption. This is the area that does not retain intact as seen from the comparison of the before and after photomicrographs. The thickness of the original sample can be readily measured by known methods, for example with an Arnes gauge. From the area of bond breakage and the thickness of the original nonwoven sheet sample, the total volume, i.e. the section, of the sample in which the bond breakage occurred can be calculated.

In addition to the bonds in the individual delaminated layers, it is necessary to obtain a measure of the bonds broken in obtaining the delaminated layers. A measure of these bonds is obtained by delaminating the samples on the Instron Tensile Tester at a strain rate of 0.05 in./min. (0.127 cm./min.) and noting the number and strength of the bonds broken over an area equal to that affected in the above tensile test. This number is then multiplied by the number of delaminations used to obtain the specimens for the tensile test. The average bond strength, number of bonds, and the variance of the bondstrength distribution are calculated from the bond strengths measured on all the delaminated layers as well as those measured during delamination. From the area of bond breakage, the thickness of the sample, and the number of bonds which have been broken, the number of bonds per cubic centimeter can be calculated.

The machine direction tongue tear strength (TIT) of a tufted nonwoven fabric for all examples but Example XIV was measured in the following manner. A nonwoven fabric tufted as in Example H is cut into a samp e 3 inches wide (cross-machine direction, across tufting rows) and 8 inches long (machinne direction, along tufting rows). The TIT of Example XIV was determined on a 6 inch by 8 inch sample. The sample is cut in the center of the width 4 inches in the machine (tufting) direction. The sample is mounted in an Instron tester using 1.5 inch by 2 inch serrated clamps. With a jaw separation of 3 inches, one side of the sample cut is mounted in the upper jaw and the other side of the sample cut is mounted in the lower jaw. The sample is uniformly spaced between the jaws. The full scale load is adjusted to a value greater than the tear strength expected for the sample. Using a crosshead speed of 12 inches per minute and a chart speed of 10 inches per minute, the Instron is started and the sample is torn. An average of the three highest stresses (one hundred units=full scale deflection) during tearing is taken. If it is not possible to obtain three peaks, the average of the peaks obtained is taken. The tongue tear strength in pounds is the average highest stress divided by and multiplied by the full scale load.

The tufted grab tensi e of a nonwoven fabric was measured in the following manner. A sample tufted as in Example II is cut into samples 4 inches wide by 6 inches long in the tufting direction. The sample is mounted in an Instron using a 1 inch by 2 inch clamp on the back side and a 1 inch square clamp in the front side at a jaw separation of 3 inches A crosshead speed of 12 inches per minute is used. The peak of the Instron curve is read and reported as pounds breaking strength.

The invention will be further illustrated by the following examples.

7 EXAMPLE 1 Two nonwoven webs of 14% low-oriented and 86% high-oriented, isotactic polypropylene filaments are bonded under different process conditions to produce two bonded sheets 1A and 1B. The high-oriented polypropylene filaments are drawn 3.5x after spinning from a polymer having a melt flow rate (MFR) (ASTM method D1238 at 230 C. with a loading of 2.16 kg.) of 12. They are 7.48 denier (0.38 tex) per filament and have a tenacity of 4.03 g.p.d. The low-oriented polypropylene filaments are drawn 1.21 X after spinning from a polymer having a MFR of 12. They are 7.73 denier (0.86 tex) per filament and have a tenacity of 1. 62 g.p.d.

The webs are prepared as fo lows: 86% of the polypropylene filaments are spun through a 30-hole spinneret at a rate of 18 g./min. total. Fourteen percent of the polypropylene filaments are spun through a -h0le spinneret at a rate of 3 g./ min. total. Each spinneret hole for both spinnerets is 0.015 inch (0.038 cm.) in diameter. The temperature of the 30-hole spinneret is 242 C. and the 5-ho1e spinneret, 220 C. The filaments from the 30- hole spinneret are led around a heated feed roll operating with a surface temperature of 118 C., and advanced by means of an idler roll canted with respect to the heated roll. A total of 5 wraps is used on the heated feed roll, which is operated with a surface speed of 243 yd./ min. (222 m./min.). The filaments leaving the heated feed roll are then passed 5 wraps around an idler ro l/ draw roll system operating cold with a surface speed of 858 yd./min. (785 m./min.). The filaments from the 5- hole spinneret are led to a heated roll operating with a surface temperature of 95 C., and a surface speed of 703 yd./min. (642 m./min.). The filaments are in contact with the heated roll for 180. The filaments leaving the heated roll are then passed to a draw roll operating cold with a surface sped of 852 yd./min. (779 m./min.). The filaments are in contact with the draw roll for 180. The filaments from both spinnerets meet and are guided so the low-oriented filaments are dispersed uniformly throughout the high-oriented filaments. The filaments are then electrostatically charged with a corona discharge device, passed into a draw jet and subsequently deposited on a moving belt to form a nonwoven web of randomly distributed continuous filaments. Two sections are cut from this product to constitute the fi amentary webs to be bonded as indicated below.

Each of the filamentary webs is bonded by passing the web at a speed of yd./min. ('9 m./ min.) while under restraint between one porous metal plate and one solid plate, each faced with cloth, for a distance of 37 inches (94 cm.) through a steam chamber in which saturated steam is maintained at superatmospheric pressure. The bonded sheets are prepared for tufting by the application of a lubricant in the following manner. The bonded sheets are submerged in a 4% aqueous dispersion of a polysiloxane which also contains 0.4% of a surface active agent (sodium alky-larylsulfonate). The sheets are then squeezed between two rolls with a nip pressure of 50 p.s.i.g. (3.5 kg./cm. at a speed of 1.5 yd./min. (1.4 m./min.) and dried in a circulating hot air oven for 45 minutes at a temperature of 93 C. The sheets are then tufted at the following conditions:

Gauge (distance between needles)0.188 in.

Speed-400 tufts/min, 7 tufts/in.

Pile yarn3700 denier (410 tex) continuous filament nylon Tuft height-0.438 in.

Type pilel0op.

Details of bonding the webs and characterization of the bonded sheets including the properties of the tufted sheets appear in Table 1. Both sheets exhibit substantial grab tensi e strength. Sheet 1A is underbonded and the values for variance and the product N are outside the limits required for acceptable performance. The tufted sheet exhibits an unsatisfactory dye-beck width loss. Sheet 13 is an example of a nonwoven sheet of this invention.

TABLE 1 Unit weight, 0z./yd. 4. 0O 3. 84 Bonding conditions:

Saturated steam pressure, p.s.i.a 66 75 Bonding contact time, secs 6. 2 6. 2

Restraint on web, lb./1n. //oz./yd. 0. 75 0. 75 Characteristics of bonded sheets:

Average bond strength (Q), grams 0. 98 1. l3

Variance (0' 2. 75 5. 35

Fiber-breaking strength (I), grams 24. 2 24. 0

N b /f Properties 01 tufted sheets:

Grab tensile, lb 164 133 Dye-beck-width loss, percent 3 1(8) Tongue tear (lbs) 342x10 g./cm. 2 11.5Xl0 g./crn. 3 1.4X10 /cm.

4 4.79Xl0 /cm.

EXAMPLE 2 A nonwoven web of 14% low-oriented and 86% highoriented, isotactic polypropylene filaments is heated to produce a bonded sheet. The high-oriented polypropylene filaments are drawn 4.0x after spinning from a polymer having a MFR of 12. They are 7.5 denier (0.83 tex) pel filament and have a tenacity of 4.20 g.p.d. The low-oriented polypropylene filaments used remain undrawn after spinning from a polymer having a MFR of 12. The filaments are 8.0 denier (0.89 tex) per filament and have a tenacity of 1.5 g.p.d. The webs are prepared as follows: 86% of the polypropylene filaments are spun through a 30-hole spinneret at a rate of 18 g./min. total. 14% of the polypropylene filaments are spun through a S-hole spinneret at a rate of 3 g./min. total. Each spinneret hole for both spinnerets is 0.015 inch (0.038 cm.) in diameter and the temperature of the 30-hole spinneret is 230 C. and the 5-hole spinneret, 224 C. The filaments from the 30-ho1e spinneret are led around a heated feed roll operating with a surface temperature of 118 C., and advanced by means of an idler roll canted with respect to the heated roll. A total of 5 wraps is used on the heated feed roll, which is operated with a surface speed of 227 yd./min. (207 m./min). The filaments leaving the heated feed roll are then passed 5 wraps around an idler roll/ draw roll system operating cold with a surface speed of 900 yd./min. (823 m./min.). The filaments from the 5-hole spinneret are led to one cold roll operating with a surface speed of 660 yd./min. (604 m./min.). The filaments are in contact with the roll for 270.

The filaments from the spinnerets are combined and then laid down as a nonwoven web as in Example 1. The filamentary web is bonded as in Example 1 with saturated steam ata pressure of p.s.i.a. (6.7 kg./cm. Properties of the bonded and tufted sheet are summarized in Table 2.The bonded sheet is lubricated and tufted as in Example 1.

TABLE 2 Unit Weight, oz./yd. (g./m. )-4.l0 (139) Characteristics of bonded sheet:

Average bond strength ()2.41 g.

Variance (a )-29.3

Fiber-breaking strength (f)-17.3 g.

N /f32.4 X10 /cm. Properties of Tufted Sheets:

Grab-Tensile, 1b. (kg.)42 (19) Dye-Beck-Width Loss-0% This bonded sheet is heavily overbonded and, after tufting, exhibits very poor grab-tensile strength. The only criterion for acceptable performance which the bonded sheet does not meet is the maximum value of N /f.

9 EXAMPLE 3 EXAMPLE 5 Three nonwoven webs of continuous, isotactic polypropylene filaments are prepared in the same general manner as that described in Example 1, except that the amount of low-oriented polypropylene filaments is varied by changing the number of those filaments, while keeping the number of high-oriented filaments constant. Identification of variables is made in Table 7. Prior to tufting, the

10 bonded sheeets are lubricated as described in Example 1.

The tufted sheets of samples 5A and 5B have a good bal- TABLE 3 High-Oriented Filaments Low-Oriented Filaments Feed Speed Draw Speed Roll Speed Bond Draw Ten., Te11., Press., Sample yd./rnin. m./min. yd./min. m./min. Ratio g.p.d. Den/F11. Tex yd./min. m./min. g.p.d. Den./Fil. Tex. p.s.i.a.

TABLE 4 Unit Weight Tuited-Grab-Tensile Dye-Beck- Width Loss, Sample oz./yd. gJm. S 0' NES f NbS/f lb. kg. Percent 3A 3.75 127 1.36 4. 93 6. 46X10 23.3 2. 77X10 138 63 2.3 3B 4. 04 137 0. 0. 14 0. 54x10 17. 7 0. 30x10 134 61 2 EXAMPLE 4 ance of grab-tensile and dye-beck-width loss. Sample 5C Three nonwoven webs of continuous, isotactic polypropylene filaments are prepared in the same general manner as in Example 1 except that the draw ratio of the 3 has high dye-beck-width loss at the same tensile value.

5 bonded sheets are summarized in Table 8.

low-oriented filaments is varied. Identification of the vari- TABLE 7 ables 1s madam Table 5. Ifnonto tuftmg, the bonded Weight percent Bonding Unit sheets are lubricated as described 1n Example 1. The three Sample Low oriented Pressure, Weight, bonded sheets meet all four structural criteria of the Elements P- -l products of this invention. These values and the properties 40 5A. 5 84 3.45 of the tufted sheets are shown in Table 6. The TIT if; g; 2 values for Samples 4A and 4B are 38 and 37 respectively. TABLE 5 High-Oriented Filaments LOW 0rieted Filaments Feed Draw Feed Draw Bond Speed, Speed, Draw Ten, Speed, Speed, Draw Ten., Press, Sample y.p.m. y.p.m. Ratio g.p.d. Den./F1l. Tex. y.p.m. y.p.m. Ratio g.p.d. Dem/F11. Tex p.s.1.a.

TABLE 6 Unit Tufted Dye-Beek- Grab- Width Loss, Sample oz./yd. S 0 N88 f NbS/f Tensile, lb. Percent 4A 4.14 1.23 7.25 11.8)(10 24.4 483x10 145 5.5 4.25 1.50 9.45 173x10 24.9 6. 95x10 123 4.3 4.03 1.41 6.71 107x10 32.1 434x10 155 3.8

TABLE 8 Tuited- Dye-Beck- Grab- Width Loss, NbS f NbS/f Tensile, lb. Percent TTT x10 23.3 515x10 107 3.8 37 9.28X104 23.0 403x10 4.0 50 239x10 21.2 113x10 114 32 44 11 EXAMPLE 6 A nonwoven web of mixed-orientation polypropylene filaments is prepared as follows: polypropylene having a MFR of 12 is spun through a 30-hole spinneret at a total 12 EXAMPLE 8 A nonwoven web of 14% (by weight) low-oriented and 86% high-oriented poly(ethylene terephthalate) filaments is prepared as follows: poly(ethylene terephthalrate of 18 g./min. Twenty-seven spinneret holes are 5 ate) (relativg viscosit y, 25.7) 1s spun through a 10-hole 1 5 f g and 3 9 spinneret at a rate of 21 g./min. total and through a 93 gi e telmgeraturedo g g 4-hole spinneret at a rate of 3.44 g./min. total. The holes are e artoun i i in both spinnerets are 0.004 in. (0.010 cm.) in diameter g Wit a f fi and the temperature of both spinnerets is 286 C. The i f d x w game i t g filaments from the l0-hole spinneret are led to a pair f f o a d FS 1s on g 523 of canted, cold feed rolls. One wrap is used on the feed f X3 5 2 2 1 2 2 23 t d rolls, which are operated with a surface speed of 1030 1: re a 5 am n S e e .2 yd./min. (942 m./min.). The filaments leaving the feed roll/draw r2118 Stem p tin z g g f an 1 5 15 rolls are then passed one wrap around a pair of canted ope a c W a Sur ace spec draw rolls operating cold with a surface speed of 4,350 of 900 yd./m1n. (823 m./m1n.). The group of 27 filayd./mm. (3,790 m./m1n.). These hlgh-orlented filaments ments has a denier of 7.2 (0.8 tex) and a tenacity of 4.14

are 5.2 denier (0.58 tex) and have a tenacity of 4.37 g.p.d., while the group of 3 filaments has a denier of 11.7

g.p.d. The filaments from the 4-hole spmneret by-pass (1.3 tex) and a tenacity of 3.46 g.p.d. th

e roll system and are mdlvldually separated by Al The drawn filaments are electrostat1cally charged W1th 1 Mag pms. These filaments are 5.3 denier (0.59 tex) and a corona discharge device, passed mto a draw et, and h ave a tenacity of 1.60 g.p.d. The filaments from both subsequently deposlted on movmg belt to form a mms innerets meet and are then electrostaticall char ed woven web of randomly distributed continuous filaments. Wpith a corona dischar d as ed t a Z E The filamentary web is bonded as in Example 1 with Subse uenfl d i g i g fi f J saturated steam at a pressure of 99 p.s.i.a. (7.0 kg./cm. waves Web i 1 s g; 2 ms Prior to tuftin'g, the bonded sheet is lubricated as in Ex- The filament a 25 conslflidet 1 3 ample 1. The sheet charcteristics and the tufted-sheet propsu orted on aylead 10th b t a t y g eed erties are summarized in Table 9. This example indicates pp er 6 Wee W0 0 S a a p of 0.225 yd./m1n. (0.206 m./mm.). The top roll 1s covered that spmnerets with varying hole sizes can be used to 4 repare 1 r0 1e ne filaments with different level of W1th a 300-mesh screen and heated to a surface temperag gs yp Py S ture of 105 C. The web is then bonded by passing it at EXAMPLE a speed of 2.67 yd./min. (2.44 m./min.) while under low A b d th d 1 restgaint betwFen tvvo polytetfraziilluoroggliyleneictiirted I30- nonwoven we is prepare wr orlente po ypromes screens or a istance o in. V cm. t roug a pylene filaments having low-oriented sections along the heated air chamber at 246 C. The bonded sheet is lubrifiber length. The polypropylene filaments are 7.02 denier cated and tufted as described in Example 1. The sheet (0.78 tex) per filament and have a tenacity of 4.11 g.p.d. characteristics and the tufted-sheet properties are sumin the higillr-oriented cisefltions, and are 8d1enierd(1.7 giarizedhin Table 9.];Ihedvg1u1ehof N /f for;i the lsheet i131- tex per ament an ave a tenaclty o g.p. in icatest at it is over on e 1s 1s m accor w1t t eo the low-oriented sections. The high-oriented segments are .10 served tufted-grab-tensile strength. The break strength of about 18 in. (46 cm.) long and the low-oriented segfibers in the bonded sheet is relatively low and this can at ments are about 2 in. (5 cm.) long. The web is prepared least partially explain both the high value of ly fi/ and as follows: Polypropylene filaments are spun through a the low tufted-grab-tensile strength. The results 1n this ex- 30-hole spinneret at a rate of 18 g./rr 1in. total. Each ample illustrate the importance of utilizing the break- :gmzreret hotle 1s (f).0hl5 in. (0.038 g1 tlliimglter and mg streggth pf tlhe fiberf1rZ1Vtl 1e/r rolrawsgoveri3 sheiet afte; blond; e empera ure 0 t e spmneret is 5 e aments ing int e ca cu ation 0 8 e ore on ing, t e 1g are led to a heated feed roll having a circumference of oriented filaments have a fiber-breaking strength of 22.7 g. 18.75 in. (47.7 cm.) with three 1.25 in. (3.17 cm.) (5.2 d.p.f. 4.37 g.p.d.) Use of this figure in the calculagrooves cut out 120 apart. The filaments are in contact tion leads to a value of 6 10 /cm. for N E/f which is with the roll for 220. The surface temperature of the 50 within the limits required for acceptable performance. roll is 130 C The roll is operated with a surface speed The high temperature used for bonding appears to have of 243 yd./m1n. (222 m./min.). The filaments leavmg caused some deorientatlon of the high-oriented filaments the heated feed roll are then passed 3 wraps around an with a resulting loss in tenacity and the formation of a idler roll/draw roll system operating cold with a sur- I sheet which is overbonded for the level of fiber-breaking face speed of 858 yd./min. (784 m./min.). The filastrength remaining after bonding. ments are then laid down as nonwoven web of randomly distributed continuous filaments as in Example 1. EXAMPLES 9 11 The filamentary web is bonded as in Example 1 with The procedures of Example 8 are followed except that saturated steam at a pressure of p.s.i.a. (4.9 kg./cm. bonding in the heated air chamber is carried out at 241 The bonded sheet is lubricated and then tufted by the 60 C. for Example 9, at 238 C. for Example 10 and at 193 procedure of Example 1. The sheet characteristics and C. for Example 11. Of these, only the product of Exthe tufted-sheet properties are summarized in Table 9. The ample 9 falls within the scope of the present invention. bonded sheet of this example has an excellent balance of Note the high dye-beck-width loss of the products of tufted-grab-tensile strength and dye-beck-width loss. Examples 10 and 11. (See Table 9.)

TABLE 9 T it dl'Zb- Dye-Beck- Bonded 0z./ Tensile, Width Loss, Sheet yd. S 1 NbS f N S/f 1b. percent 1.21 8.4 154x10 21.5 7.1 10 1.3 4 1.95 17.3 7. 51 10 25.7 2 92x10 165 3.5 4 1. 83 5.64 1115x10 9.2 141x10 a1 3.5 2.0 6.7 128x10 20,9 6. 2x10 5.0 0.88 1.4 3.4x10 -1.6 10 153 16 Ex. 11 3.88 0.55 0.47 1.1 10 .5 10 132 as 11 Estimated NorawTTl values for Examples 6, 7, 8, 9, 10, and 11 are 31, 50, 21, 80, 42 and 43 respectlvely.

The graphs in FIGURES 1, 2, 3, and 4 are based on the data obtained in Examples 1-8, and additional cumulative data obtained with other similar bonded nonwoven sheet materials. The data are plotted and the best-fit lines are then drawn to illustrate the relationship between the tufted-sheet properties and the structural characteristics of the bonded nonwoven sheet materials.

EXAMPLE 12 An isotactic polypropylene web of 4 in. (10 cm.) staple fibers (8 d.p.f.) (0.9 tex) is made on a Garnett card and bonded at 78 p.s.i.a. (5.5 kg./cm. Fifteen percent of the fibers are 1.5 g.p.d. and the remainder, 4.0 g.p.d. A polysiloxane lubricant is applied to the bonded sheet. The tufted properties are 97 lbs. (44 kg.) grab tensile (unit weight 3.6 oz./yd. (122 gm./m. and a dye-beck-width loss of Characterization of the bonded sheet is as follows:

Web A 157.5" C.

Web B 159.3" C.

The binder concentration was calculated to be about 24% by weight. The bonded webs were lubricated and then tufted. The bond strength distribution parameters prior to tufting and tufted grab tensile values for the tufted sheets appear in Table 10 below.

TABLE 10 Web oz./yd. Pickup (1bs.) (gms.) (gms./cc.) (cc.- (lbs.)

A 4.1 2.0 122 2.7 21.6 9.5x10 3.1x10 53 B 4.0 1.9 92 1.9 19.0 11.1 10 s.0 10- 44 TTT=Tuited Tongue Tear (machine direction); TGT=Tufted Grab Tensile (cross machine direction); =Average Bond Strength; v =Variance; N =Number of bonds per cubic centimeter with strength greater than 0.1 gm.; f=Fiber breaking strength, grams filament.

This example illustrates the relative insensitivity of the bonded nonwoven sheets of this invention to the condition of the tufting needles. For comparison, the results obtained with nonwoven carpet backing prepared by self-bonding nonwoven webs of like continuous filaments of isotactic polypropylene are also presented. The nonwoven sheets are comparable in all respects except that the nonwoven sheet of this invention is prepared by bonding a nonwoven web of mixed-orientation polypropylene filaments while the control sheet is prepared by selfbonding the nonwoven web of polypropylene filaments all having the same level of orientation. The high-oriented filaments of the mixed-orientation web have the same level of orientation as the filaments in the control sheet. The grab-tensile strengths of bonded and lubricated nonwoven sheets after tufting with new and damaged needles are summarized below for two series of tests.

Tufted-Grab-Tensile, lb. (kg.)

Nonwoven Control,

A random unbonded unconsolidated web of polypropyl ene fibers was collected between pieces of porous cloth. The fibers (9 d.p.f.) had a breaking strength of 3025 What is claimed is:

1. A bonded nonwoven sheet comprising a matrix of synthetic organic fibers having a breaking strength of at least 7 grams, said fibers being interconnected at a multiplicity of points throughout the sheet, by at least some bonds having a strength greater than 0.1 gram, the average strength of these bonds being at least 029 gram and less than the matrix fiber breaking strength, the said bond strength distribution being characterized by a variance of at least 4, the number of said bonds being such that the product of the number of bonds per cubic centimeter and the average bond strength is greater than 5 x10' g./cm. and this product divided by the fiber breaking strength is less than 9 l0 /cm.

2. The product of claim 1 wherein the matrix fiber is isotactic polypropylene of high orientation.

3. The product of claim 2 which additionally contains polypropylene fiber of low orientation as a binder fiber.

4. The product of claim 3 wherein the matrix and binder fibers are sections along the length of single filaments.

5. The product of claim 1 wherein the fiber denier is between 3 and 15.

6. A bonded nonwoven sheet comprising matrix and binder fiber, said matrix fiber being synthetic organic fibers having an average breaking strength of at least 7 grams, the fibers of the sheet being interconnected at a multiplicity of points throughout the sheet by at least some bonds having a strength greater than 0.1 gram, the average strength of said "bonds being at least 0.9 gram and less than the matrix fiber breaking strength, the strength distribution of said bonds being characterized by a variance of at least 4, the number of said bonds being such that the product of the number of bonds per cubic centimeter and the average bond strength'is greater than 5 X 10 g./cm. and this product divided by the fiber breaking strength is less than 9X10 /cm.

7. The product of claim 6 wherein the matrix and binder fiber are polypropylene of high and low orientation respectively.

8. The sheet of claim 1 wherein the synthetic organic FOREIGN PATENTS fibers are continuous filaments. 808,287 2/1959 Great Britain 844,760 8/1960 Great Britain.

UNITED STATES PATENTS ROBERT F. BURNETT, Prlmary Exarnmer L. M. CARLIN, Assistant Examiner 3,193,442 7/1965 Schulz et a1. 161169 3,276,944 10/1966 Levy 161 170 US. Cl. X.R. 3,396,071 8/1968 Couzens 161 17O 161-170 References Cited @2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 502,538 Dated E/ jY Inventor(s) Joseph Claine Petersen It is certified that error appears in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

Column 5, line 49, "narow should read "narrow".

Column 6, line 15, "retain" should read -remain--.

Column 6, line 44, "machinne" should read --ma.chine-.

Column 6, line 71, put a period after inches".

Column 7, line 9, "0.38" should read --O.83--.

Column 9, Table 6, 6th column, third number, "32.1" should read --23.l--.

Column 10, Table last column, second number, "2" should read -22.

Column 12, line 17, "3,790" should read --3,97o--.

Edwaflnflatchml mm 1:. mm, m.

Mm Gomisaioner d: Patents J 

